Isoprene and Rubber. XXIV. The Reduction of Rubber with Hydriodic Acid

In the past, the reduction of rubber has been of special interest since Harries was of the opinion, based on his ideas on the constitution of rubber, that hydrorubber might possibly be distilled without decomposition in vacua, and therefore that its preparation would be of importance in explaining the constitution of rubber. Staudinger and Fritschi obtained a hydrorubber by catalytic reduction, which they considered to be a high molecular paraffin hydrocarbon; in the distillation it cracked and yielded low molecular cleavage products. It was concluded from this that rubber must also be a high molecular hydrocarbon. Contrary to this opinion, there was the evidence that the hydrorubber had the same appearance as rubber and dissolved readily in solvents like ether, and therefore showed essential differences from high molecular paraffins of known constitution as, for example, dimyricyl. Since hydrorubber has a branched chain, it might be thought that it differed from dimyricyl on this account. It was surprising, however, that in the reduction of butadiene rubber the hydrogenation product obtained likewise does not possess the physical properties of a high molecular paraffin hydrocarbon, although here properties similar to those of high molecular paraffins are to be expected, since a normal paraffin chain should result from the reduction of butadiene rubber. These problems were sufficient inducement for preparing hydrorubber in still another way. Berthelot had already many years ago converted rubber with hydriodic acid at an elevated temperature into paraffin hydrocarbons, which distilled above 350° without decomposition. One might assume, therefore, that there is perhaps in this substance the true hydrogenation product of rubber which was sought by Harries, whereas in catalytic hydrogenation the rubber micelle assumed by Harries is not completely split up.